C4 auto not going into 3rd
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C4 auto not going into 3rd
Hey all,
I'm having trouble with my C4 with only 50 rebuilt miles (hooked to a 300) shifting from 2 to 3rd. It is fine from 1st to 2nd. Also, when in 2nd and you let off the gas, it does not shift into neutral, it stays in 2nd. I have had this problem awhile, but have not addressed it as the truck was not street legal until recently. Last week though it did shift fine into 3rd, but is playing games again today.
Fluid level is fine, vacuum at modulator is 18" hg, modulator is tuned for the proper shift points. I did adjust it counter clockwise but the 1st to 2nd shift was too quick and still did not go into 3rd so I turned it back.
I've read several previous threads, but could not find a similar problem discussed. Any ideas???
Thanks
I'm having trouble with my C4 with only 50 rebuilt miles (hooked to a 300) shifting from 2 to 3rd. It is fine from 1st to 2nd. Also, when in 2nd and you let off the gas, it does not shift into neutral, it stays in 2nd. I have had this problem awhile, but have not addressed it as the truck was not street legal until recently. Last week though it did shift fine into 3rd, but is playing games again today.
Fluid level is fine, vacuum at modulator is 18" hg, modulator is tuned for the proper shift points. I did adjust it counter clockwise but the 1st to 2nd shift was too quick and still did not go into 3rd so I turned it back.
I've read several previous threads, but could not find a similar problem discussed. Any ideas???
Thanks
Lead Driver
Joined: Jul 2011
Posts: 8,679
Likes: 191
From: On the Edge of the Desert
Originally Posted by Alabama Style
Hey all,
I'm having trouble with my C4 with only 50 rebuilt miles (hooked to a 300) shifting from 2 to 3rd. It is fine from 1st to 2nd. Also, when in 2nd and you let off the gas, it does not shift into neutral, it stays in 2nd. I have had this problem awhile, but have not addressed it as the truck was not street legal until recently. Last week though it did shift fine into 3rd, but is playing games again today.
Fluid level is fine, vacuum at modulator is 18" hg, modulator is tuned for the proper shift points. I did adjust it counter clockwise but the 1st to 2nd shift was too quick and still did not go into 3rd so I turned it back.
I've read several previous threads, but could not find a similar problem discussed. Any ideas???
Thanks
I'm having trouble with my C4 with only 50 rebuilt miles (hooked to a 300) shifting from 2 to 3rd. It is fine from 1st to 2nd. Also, when in 2nd and you let off the gas, it does not shift into neutral, it stays in 2nd. I have had this problem awhile, but have not addressed it as the truck was not street legal until recently. Last week though it did shift fine into 3rd, but is playing games again today.
Fluid level is fine, vacuum at modulator is 18" hg, modulator is tuned for the proper shift points. I did adjust it counter clockwise but the 1st to 2nd shift was too quick and still did not go into 3rd so I turned it back.
I've read several previous threads, but could not find a similar problem discussed. Any ideas???
Thanks
It's not supposed to go into neutral when it's in gear... what do you mean???
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Yes, the modulator was replaced, but that was over 3 years ago. I would start the truck once a month or so and shift through the gears while stationary, just to 'move the fluid' around.
What I mean is when I am in Drive and get up to 25 mph or so and still in 2nd gear, then let off of the gas, she stays in 2nd while decelerating instead of 'freewheeling?". I might not be saying it right, but in drive, when you slow then stop, it should be able to coast and it automatically goes back to first when you stop. Mine stays in 2nd and acts like I'm downshifting.
What I mean is when I am in Drive and get up to 25 mph or so and still in 2nd gear, then let off of the gas, she stays in 2nd while decelerating instead of 'freewheeling?". I might not be saying it right, but in drive, when you slow then stop, it should be able to coast and it automatically goes back to first when you stop. Mine stays in 2nd and acts like I'm downshifting.
Lead Driver
Joined: Apr 2011
Posts: 6,399
Likes: 40
From: El Dorado, Arkansas
If you have a vacuum gauge, take the rubber vacuum line loose from the modulator and plug the hose off. Attach the vacuum gauge to the line at the manifold end of the line and see if it will build/hold a vacuum. If not, there's a leak in the line going to the modulator.
Attach the vacuum gauge to the modulator itself and see if it'll hold a vacuum. If not, the modulator is bad.
If both of these check out, then the problem may lie in the valve body of the transmission.
Attach the vacuum gauge to the modulator itself and see if it'll hold a vacuum. If not, the modulator is bad.
If both of these check out, then the problem may lie in the valve body of the transmission.
Lead Driver
Joined: Apr 2011
Posts: 6,399
Likes: 40
From: El Dorado, Arkansas
If the pan on the C4 is stock and unmodified, there won't be a drain plug to pull a sample from. If the pan is loosened, the transmission fluid is going to come gushing out and you'll probably wind up with a leaky gasket if you try to tighten the pan back up with the same gasket --particularly if it's a cork gasket and not a neoprene gasket.
About your only other alternative to getting a fluid sample from the transmission would be to run a small hose down the dipstick tube and suction some fluid out with a vacuum pump or, if the converter has a drain plug.
Otherwise, it would be a matter of dropping the pan, drain all the fluid and check for metal shavings.
About your only other alternative to getting a fluid sample from the transmission would be to run a small hose down the dipstick tube and suction some fluid out with a vacuum pump or, if the converter has a drain plug.
Otherwise, it would be a matter of dropping the pan, drain all the fluid and check for metal shavings.
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Lead Driver
Joined: Jul 2011
Posts: 8,679
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From: On the Edge of the Desert
I dont think it's supposed to freewheel until very low speed. It's been a few years since I took my c4 out. I don't remember exactly how it behaved other than good.
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Lead Driver
Joined: Feb 2002
Posts: 7,958
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From: Greater Austin, Texas
I am wondering if your manual linkage is not adjusted correctly and you are in 2nd on the manual valve when you think you are in Drive? On the C4, if you shift it into 2nd, it stays in 2nd always, even starts off in 2nd.
Cargo Master
Joined: Sep 2007
Posts: 2,470
Likes: 535
From: Chandler, AZ
If the pan on the C4 is stock and unmodified, there won't be a drain plug to pull a sample from. If the pan is loosened, the transmission fluid is going to come gushing out and you'll probably wind up with a leaky gasket if you try to tighten the pan back up with the same gasket --particularly if it's a cork gasket and not a neoprene gasket.
About your only other alternative to getting a fluid sample from the transmission would be to run a small hose down the dipstick tube and suction some fluid out with a vacuum pump or, if the converter has a drain plug.
Otherwise, it would be a matter of dropping the pan, drain all the fluid and check for metal shavings.
About your only other alternative to getting a fluid sample from the transmission would be to run a small hose down the dipstick tube and suction some fluid out with a vacuum pump or, if the converter has a drain plug.
Otherwise, it would be a matter of dropping the pan, drain all the fluid and check for metal shavings.
Another option is to remove the cooler return line from the back of the tranny, run a hose from it into a bucket, and start the engine to pump out a 1/2 a quart or so.
I would check the linkage first though, as stated above
Hotshot
Joined: Mar 2013
Posts: 14,255
Likes: 199
From: Phoenix, Az.
2X. The manual control linkage is the 1st thing I thought of also. That and the kick down rod. Make sure the kick down rod is connected to the carb correctly. If the kick down rod is shoved down out of the way the tranny is going to think you want passing gear.
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